Golf balls with polyurethane covers formed from low-monol content polyols

ABSTRACT

Disclosed herein, in various embodiments, is a golf ball having a polyurethane cover formed from a low-monol content polyol. The low-monol content polyol is preferably a polyether polyol. The golf ball is preferably a three-piece solid golf ball with a core, mantle layer and a cover. A low-monol content is preferably less than 1%. More preferably, the low-monol content is between 0.5% to 1%.

CROSS REFERENCES TO RELATED APPLICATIONS

The Present Application claims priority to U.S. Provisional Patent Application No. 60/824,315, filed Sep. 1, 2006.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates, in various embodiments, to polyurethane covered golf balls formed from a low-monol content polyol.

2. Description of the Related Art

Golf balls have been generally categorized into three different groups. These groups are, namely, one-piece or unitary balls, wound balls, and multi-piece solid balls.

A one-piece ball typically is formed from a solid mass of moldable material, such as an elastomer, which has been cured to develop the necessary degree of hardness, durability, etc., desired. The one-piece ball generally possesses the same overall composition between the interior and exterior of the ball. One piece balls are described, for example, in U.S. Pat. No. 3,313,545; U.S. Pat. No. 3,373,123; and U.S. Pat. No. 3,384,612.

A wound ball has frequently been referred to as a “three-piece ball” since it is produced by winding vulcanized rubber thread under tension around a solid or semi-solid center to form a wound core. The wound core is then enclosed in a single or multi-layer covering of tough protective material. Until relatively recently, the wound ball was generally desired by many skilled, low handicap golfers due to a number of characteristics, i.e., feel, playability, etc.

For example, the three-piece wound ball has been produced utilizing a balata, or balata like, cover material which is relatively soft and flexible. Upon impact, it compresses against the surface of the club producing high spin. Consequently, the soft and flexible balata covers along with wound cores provide an experienced golfer with the ability to apply a spin to control the ball in flight in order to produce a draw or a fade or a backspin which causes the ball to “bite” or stop abruptly on contact with the green. Moreover, the balata cover produces a soft “feel” to the low handicap player. Such playability properties of workability, feel, etc., are particularly important in short iron play and low swing speeds and are exploited significantly by highly skilled players.

However, a three-piece wound ball has several disadvantages both from a manufacturing standpoint and a playability standpoint. In this regard, a thread wound ball is relatively difficult to manufacture due to the number of production steps required and the careful control which must be exercised in each stage of manufacture to achieve suitable roundness, velocity, rebound, “click”, “feel”, and the like.

Additionally, a soft thread wound (three-piece) ball is not well suited for use by the less skilled and/or high handicap golfer who cannot intentionally control the spin of the ball. For example, the unintentional application of side spin by a less skilled golfer produces hooking or slicing. The side spin reduces the golfer's control over the ball as well as reduces travel distance.

Similarly, despite all of the benefits of balata, balata covered balls are easily “cut” and/or damaged if mishit. Consequently, golf balls produced with balata or balata containing cover compositions can exhibit a relatively short life span. As a result of this negative property, balata and its synthetic substitute, trans-polyisoprene, and resin blends, have been essentially replaced as the cover materials of choice by golf ball manufacturers by materials comprising ionomeric resins and other elastomers such as polyurethanes.

Multi-piece solid golf balls, on the other hand, include a solid resilient core and a cover having single or multiple layers employing different types of material molded on the core. The core can also include one or more layers. Additionally, one or more intermediate, or mantle, layers can also be included between the core and cover layer(s).

By utilizing different types of materials and different construction combinations, multi-piece solid golf balls have now been designed to match and/or surpass the beneficial properties produced by three-piece wound balls. Additionally, the multi-piece solid golf balls do not possess the manufacturing difficulties, etc., that are associated with the three-piece wound balls.

As a result, a wide variety of multi-piece solid golf balls are now commercially available to suit an individual player's game. In essence, different types of balls have been, and are being, specifically designed to suit various skill levels. Moreover, improved golf balls are continually being produced by golf ball manufacturers with technological advancements in materials and manufacturing processes.

In the past, the molding processes used for forming the cover and/or the intermediate or mantle layer of a golf ball usually involved either compression molding or injection molding techniques.

In compression molding, the golf ball core is inserted into a central area of a two piece die and pre-sized sections of cover material are placed in each half of the die, which then clamps shut. The application of heat and pressure molds the cover material about the core.

Polymeric materials, or blends thereof, have been used for modern golf ball covers because different grades and combinations offer certain levels of hardness, damage resistance when the ball is struck with a club, and elasticity, thereby providing responsiveness when hit. Some of these materials facilitate processing by compression molding, yet disadvantages have also arisen. These disadvantages include the presence of seams in the cover, which occur where the pre-sized sections of cover material are joined, and high process cycle times which are required to heat the cover material and complete the molding process.

Injection molding of golf ball covers arose as a processing technique to overcome some of the disadvantages of compression molding. The process basically involves inserting a golf ball core into a die, closing the die and forcing a heated, viscous polymeric material into the die. The material is then cooled and the golf ball is removed from the die. Injection molding is well-suited for thermoplastic materials, but has generally limited applications with some thermosetting polymers. However, several of these thermosetting polymers often exhibit the hardness and elasticity properties desired in golf ball cover construction.

Furthermore, some of the most promising thermosetting materials are reactive, requiring two or more components to be mixed and rapidly transferred into a die before a polymerization reaction is complete. As a result, traditional injection molding techniques do not provide proper processing when applied to these materials.

Reaction injection molding (“RIM”) is a processing technique used specifically for certain reactive thermosetting polymers. By “reactive” it is meant that the polymer is formed from two or more components which react. Generally, the components, prior to reacting, exhibit relatively low viscosities. The low viscosities of the components allow the use of lower temperatures and pressures than those utilized in traditional injection molding. In reaction injection molding, the two or more components are combined and react to produce the final polymerized material.

A high amount of monohydroxy functional species (“monol”) present in a polyol component of a polyurethane system is detrimental in forming a high molecular weight polyurethane. A monohydroxy functional species is a chain terminator, which results in a lower molecular weight. BAYER has a polyol sold under the ACCLAIM brand name which has a low Mole % monol content. According to Bayer, monol content for a polyol can be calculated using the formula set forth below:

$f = \frac{\left( {{OH}/56.1} \right)}{{\left\{ {\left( {{OH}/56.1} \right) - {unsat}} \right\} \left( {1/f_{n}} \right)} + {unsat}}$

Wherein

-   -   f=functionality     -   OH=Hydroxyl number, mg KOH/g     -   Unsat=Unsaturation, meq/g     -   f_(n)=nominal functionality, (e.g. 3 for triol).

However, it is difficult to find a RIM system that can use a low monol content polyol. Due to the continuous importance of improving the properties of a golf ball, it would be beneficial to make a multi-layer golf ball, such as a RIM covered multi-layer golf ball, that exhibits improved properties for certain golfers.

These and other non-limiting objects and features of the disclosure will be apparent from the following description and from the claims.

BRIEF SUMMARY OF THE INVENTION

The invention is directed to a golf ball having an outer cover comprising polyurethane. This polyurethane cover may be of the crosslinkable or thermoplastic type. The urethane is prepared by reacting a diisocyanate with a polyol and a chain extender. Diisocyanates are known in the art and any of those commonly used in the polyurethane elastomer art may be used.

Examples of diisocyanates suitable for use in the present invention include, but are not limited to, aromatic diisocyanates such as 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, mixtures thereof, 4,4′diphenylmethane diisocyanate, m-phenylene diisocyanage, and 4,4′-biphenyl diisocyanate; aliphatic diisocyanates such as tetramethylene diisocyanage, hexamethylene diisocyanate (HDI), and octamethylene diisocyanate; and alicyclic diisocyanates such as xylene diisocyanate. A preferred diisocyanate for use in the present invention is 4,4′diphenylmethane diisocyanate.

Chain extenders are known in the polyurethane elastomer art. Examples of chain extenders suitable for use in the present invention include, but are not limited to, 1,4-butylene glycol, 1,2-ethylene glycol, 1,2-butane diol, 1,6-hexane diol, 2,2-dimethyl-1,3-propane diol, 4,4′-diaminodiphenylmethane, hydrogenated MDA, isophorone diamine, hexamethylenediamine, and hydroquinone diethylol ether. The chain extenders preferably have a molecular weight of about 10 to about 1000. A preferred polyol for use in the present invention is a poly(propylene glycol)-based polyol. Furthermore, the poly(propylene glycol)-based polyol has a low mono-functional hydroxyl terminated (monol) content (preferably, less than about 0.001 milliequivalents/gram), resulting in improved mechanical properties over urethanes produced from similar conventional poly(propylene glycol)-based polyols. Examples of mechanical properties which may be improved using the polyurethane of the present invention include tensile strength and elongation.

Low monol content polyols are known to improve the performance characteristics of urethanes. Conventional poly(propylene glycol)-based polyols have a considerable monol content, and these monols act as polymer chain terminators rather than propagating species. Chain terminating species limit the molecular weight of the polymer and consequently, the mechanical properties.

The process of making low monol content polyols has resulted in higher overall molecular weight of the polyols. This higher molecular weight polyol has been shown to improve phase separation, thus improving performance. Through proper formulation, soft, elastomeric urethane systems offering high elongations and improved mechanical properties over conventional urethane systems may be produced. High modulus systems may also be produced using the same polyols.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a cross-sectional view of one exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a multi-layer golf ball 10 is illustrated. In this embodiment, golf ball 10 comprises core 12, mantle 14, and cover 16. A description of low-monol content polyols is provided in Improved Processability And Performance in MDI Elastomers Based on Ultra-Low Monol Polyols, Lawrey and Barkesby, Polyurethanes Expo 2003, Oct. 1-3, 2003, page 260-267, which is hereby incorporated by reference in its entirety.

Ultra-low monol content polyols are available from Bayer Corporation. One such preferred material is ACCLAIM 2200, which is a polyether poloy and another such product is ACCLAIM 3300N polyol, which is an ultra-low monol triol. Low monol content can be less than 1%, and more preferably from 1% to 0.5%.

One preferred cover formulation is formed from a diisocyanate component and a polyol component. The poly component preferably includes 100 parts ACCLAIM 2200 with a monol content of less than 1%, 11.5 parts Ethacure 100LC, 1.0 parts Dabco T-12, 1.5 parts Dabco 33LV. The diisocyanate component is preferably Isonate 181 with 23% NCO group content.

Two principal properties involved in golf ball performance are resilience and compression. Resilience is determined by the coefficient of restitution (COR), i.e., the constant “e” which is the ratio of the relative velocity of an elastic sphere after direct impact to that before impact. As a result, the coefficient of restitution (“e”) can vary from 0 to 1, with 1 being equivalent to a perfectly or completely elastic collision and 0 being equivalent to a perfectly or completely inelastic collision.

Resilience, along with additional factors such as club head speed, angle of trajectory, and ball construction and surface configuration (i.e., dimple pattern), generally determines the distance a ball will travel when hit. Since club head speed and the angle of trajectory are factors not easily controllable by a manufacturer, factors of concern among manufacturers are the COR, the ball construction and the surface configuration of the ball.

The COR in solid core balls is a function of the composition of the molded core and of the cover. In balls containing a wound core (i.e., balls comprising a liquid or solid center, elastic windings, and a cover), the COR is a function of not only the composition of the center and the cover, but also the composition and tension of the elastomeric windings.

The COR is the ratio of the outgoing velocity to the incoming velocity. In the examples of this application, the COR of a golf ball was measured by propelling a ball horizontally at a speed of 125±1 feet per second (fps) against a generally vertical, hard, flat steel plate and measuring the ball's incoming and outgoing velocity electronically. Speeds were measured with a pair of Ohler Mark 55 ballistic screens, which provide a timing pulse when an object passes through them. The screens are separated by 36 inches and are located 25.25 inches and 61.25 inches from the rebound wall. The ball speed was measured by timing the pulses from screen 1 to screen 2 on the way into the rebound wall (as the average speed of the ball over 36 inches), and then the exit speed was timed from screen 2 to screen 1 over the same distance. The rebound wall was tilted 2 degrees from a vertical plane to allow the ball to rebound slightly downward in order to miss the edge of the cannon that fired it.

As indicated above, the incoming speed should be 125±1 fps. Furthermore, the correlation between COR and forward or incoming speed has been studied and a correction has been made over the ±1 fps range so that the COR is reported as if the ball had an incoming speed of exactly 125.0 fps.

Compression is another important property involved in the performance of a golf ball. The compression of the ball can affect the playability of the ball on striking and the sound or “click” produced. Similarly, compression can affect the “feel” of the ball (i.e., hard or soft responsive feel), particularly in chipping and putting.

Moreover, while compression itself has little bearing on the distance performance of a ball, compression can affect the playability of the ball on striking. The degree of compression of a ball against the club face and the softness of the cover influences the resultant spin rate.

The term “compression” utilized in the golf ball trade generally defines the overall deflection that a golf ball undergoes when subjected to a compressive load. For example, compression indicates the amount of change in golf ball's shape upon striking. The development of solid core technology in two-piece or multi-piece solid balls has allowed for much more precise control of compression in comparison to thread wound three-piece balls. This is because in the manufacture of solid core balls, the amount of deflection or deformation is precisely controlled by the chemical formula used in making the cores. This differs from wound three-piece balls wherein compression is controlled in part by the winding process of the elastic thread. Thus, two-piece and multi-layer solid core balls exhibit much more consistent compression readings than balls having wound cores such as the thread wound three-piece balls.

In the past, PGA compression related to a scale of from 0 to 200 given to a golf ball. The lower PGA compression value, the softer the feel of the ball upon striking. In practice, tournament quality balls have compression ratings around 40 to 110, and preferably around 50 to 100.

In determining PGA compression using the 0 to 200 scale, a standard force is applied to the external surface of the ball. A ball which exhibits no deflection (0.0 inches in deflection) is rated 200 and a ball which deflects 2/10th of an inch (0.2 inches) is rated 0. Every change of 0.001 of an inch in deflection represents a 1 point drop in compression. Consequently, a ball which deflects 0.1 inches (100×0.001 inches) has a PGA compression value of 100 (i.e., 200 to 100) and a ball which deflects 0.110 inches (110×0.001 inches) has a PGA compression of 90 (i.e., 200 to 110). In order to assist in the determination of compression, several devices have been employed by the industry. For example, PGA compression is determined by an apparatus fashioned in the form of a small press with an upper and lower anvil. The upper anvil is at rest against a 200-pound die spring, and the lower anvil is movable through 0.300 inches by means of a crank mechanism. In its open position, the gap between the anvils is 1.780 inches, allowing a clearance of 0.200 inches for insertion of the ball. As the lower anvil is raised by the crank, it compresses the ball against the upper anvil, such compression occurring during the last 0.200 inches of stroke of the lower anvil, the ball then loading the upper anvil which in turn loads the spring. The equilibrium point of the upper anvil is measured by a dial micrometer if the anvil is deflected by the ball more than 0.100 inches (less deflection is simply regarded as zero compression) and the reading on the micrometer dial is referred to as the compression of the ball. When golf ball components (i.e., centers, cores, mantled core, etc.) smaller than 1.680 inches in diameter are utilized, metallic shims are included to produce the combined diameter of the shims and the component to be 1.680 inches.

An example to determine PGA compression can be shown by utilizing a golf ball compression tester produced by OK Automation, Sinking Spring, Pa. (formerly, Atti Engineering Corporation of Newark, N.J.). The compression tester produced by OK Automation is calibrated against a calibration spring provided by the manufacturer. The value obtained by this tester relates to an arbitrary value expressed by a number which may range from 0 to 100, although a value of 200 can be measured as indicated by two revolutions of the dial indicator on the apparatus. The value obtained defines the deflection that a golf ball undergoes when subjected to compressive loading. The Atti test apparatus consists of a lower movable platform and an upper movable spring-loaded anvil. The dial indicator is mounted such that is measures the upward movement of the spring-loaded anvil. The golf ball to be tested is placed in the lower platform, which is then raised a fixed distance. The upper portion of the golf ball comes in contact with and exerts a pressure on the spring-loaded anvil. Depending upon the distance of the golf ball to be compressed, the upper anvil is forced upward against the spring.

Furthermore, additional compression devices may also be utilized to monitor golf ball compression such as a Whitney Tester, Whitney Systems, Inc., Chelsford, Mass., or an Instron Device, Instron Corporation, Canton, Mass. Herein, compression was measured using an Instron™ Device (model 5544), Instron Corporation, Canton, Mass. Compression of a golf ball, core, or golf ball component is measured to be the deflection (in inches) caused by a 200 lb. load applied in a Load Control Mode at the rate of 15 kips, and approach speed of 20 inches per minute, with a preload of 0.2 lbf plus the system compliance of the device.

As used herein, “Shore D hardness” of a cover is measured generally in accordance with ASTM D-2240, except the measurements are made on the curved surface of a molded cover, rather than on a plaque. Furthermore, the Shore D hardness of the cover is measured while the cover remains over the core. When a hardness measurement is made on a dimpled cover, Shore D hardness is measured at a land area of the dimpled cover.

“Shore B hardness” is similar to “Shore D hardness” set forth above, except a different tension on the stylus is utilized. This tension is lower to avoid puncturing the material which may occur when softer materials are being measured.

A “Mooney unit” is an arbitrary unit used to measure the plasticity of raw or unvulcanized rubber. The plasticity in Mooney units is equal to the torque, measured on an arbitrary scale, on a disk in a vessel that contains rubber at a temperature of 212° F. (100° C.) and that rotates at two revolutions per minute. The measurement of Mooney viscosity, i.e. Mooney viscosity [ML₁₊₄ (100° C.], is defined according to the standard ASTM D-1646, herein incorporated by reference. In ASTM D-1646, it is stated that the Mooney viscosity is not a true viscosity, but a measure of shearing torque over a range of shearing stresses. Measurement of Mooney viscosity is also described in the Vanderbilt Rubber Handbook, 13th Ed., (1990), pages 565-566, also herein incorporated by reference. Generally, polybutadiene rubbers have Mooney viscosities, measured at 212° F., of from about 25 to about 65. Instruments for measuring Mooney viscosities are commercially available such as a Monsanto Mooney Viscometer, Model MV 2000. Another commercially available device is a Mooney viscometer made by Shimadzu Seisakusho Ltd.

As used herein, the term “phr” refers to the number of parts by weight of a particular component in an elastomeric or rubber mixture, relative to 100 parts by weight of the total elastomeric or rubber mixture.

The core 12 of the golf ball of the present disclosure is a relatively hard, high compression, molded core. In embodiments, it is a molded core comprising a polybutadiene composition containing at least one curing agent. Polybutadiene has been found to be particularly useful because it imparts to the golf balls a relatively high COR. Polybutadiene can be cured using a free radical initiator such as a peroxide. A broad range for the Mw of the polybutadiene composition is from about 50,000 to about 1,000,000; a narrower range is from about 50,000 to about 500,000. A high cis-polybutadiene, such as a cis-1-4-polybutadiene, is preferably employed, or a blend of high cis-1-4-polybutadiene with other elastomers may also be utilized. In specific embodiments, a high cis-1-4-polybutadiene having a Mw of from about 100,000 to about 500,000 is employed.

A specific polybutadiene which may be used in the core of certain embodiments of the present disclosure features a cis-1,4 content of at least 90% and preferably greater than 96% such as Cariflex® BR-1220 currently available from Dow Chemical, France; and Taktene® 220 currently available from Bayer, Orange, Tex.

For example, Cariflex® BR-1220 polybutadiene and Taktene® 220 polybutadiene may be utilized alone, in combination with one another, or in combination with other polybutadienes. Generally, these other polybutadienes have Mooney viscosities in the range of about 25 to 65 or higher. ooney viscosity polybutadiene suitable for use with the present development includes Cariflex® BCP 820, from Shell Chimie of France. Although this polybutadiene produces cores exhibiting higher COR values, it is somewhat difficult to process using conventional equipment.

Examples of further polybutadienes include those obtained by using a neodymium-based catalyst, such as Neo C is 40 and Neo C is 60 from Enichem, Polimeri Europa America, 200 West Loop South, Suite 2010, Houston, Tex. 77027, and those obtained by using a neodymium based catalyst, such as CB-22, CB-23, and CB-24 from Bayer Co., Pittsburgh, Pa.

Alternative polybutadienes include fairly high Mooney viscosity polybutadienes including the commercially available BUNA® CB series polybutadiene rubbers manufactured by the Bayer Co., Pittsburgh, Pa. The BUNA® CB series polybutadiene rubbers are generally of a relatively high purity and light color. The low gel content of the BUNA® CB series polybutadiene rubbers ensures almost complete solubility in styrene. The BUNA® CB series polybutadiene rubbers have a relatively high cis-1,4 content. Preferably, each BUNA® CB series polybutadiene rubber has a cis-1,4 content of at least 96%. Additionally, each BUNA® CB series polybutadiene rubber exhibits a different solution viscosity, preferably from about 42 mPa·s to about 170 mPa·s, while maintaining a relatively constant solid Mooney viscosity value range, preferably of from about 38 to about 52. The BUNA® CB series polybutadiene rubbers preferably have a vinyl content of less than about 12%, more preferably a vinyl content of about 2%. In this regard, below is a listing of commercially available BUNA® CB series polybutadiene rubbers and the solution viscosity and Mooney viscosity of each BUNA® CB series polybutadiene rubber.

In addition to the polybutadiene rubbers noted above, BUNA® CB 10 polybutadiene rubber is also very desirous to be included in the composition of the present development. BUNA® CB 10 polybutadiene rubber has a relatively high cis-1,4 content, good resistance to reversion, abrasion and flex cracking, good low temperature flexibility and high resilience. The BUNA® CB 10 polybutadiene rubber preferably has a vinyl content of less than about 12%, more preferably about 2% or less.

The polybutadiene utilized in the present development can also be mixed with other elastomers. These include natural rubbers, polyisoprene rubber, SBR rubber (styrene-butadiene rubber) and others to produce certain desired core properties.

The elastomeric rubber composition also includes a curing agent. The curing agent is the reaction product of a carboxylic acid or acids and an oxide or carbonate of a metal such as zinc, magnesium, barium, calcium, lithium, sodium, potassium, cadmium, lead, tin, and the like. Exemplary unsaturated carboxylic acids are acrylic acid, methacrylic acid, itaconic acid, crotonic acid, sorbic acid, and the like, and mixtures thereof. Usually, the selected acid is either acrylic or methacrylic acid. From about 15 to about 50, and specifically from about 17 to about 35 parts by weight of the carboxylic acid salt, such as zinc diacrylate (ZDA), is included per 100 parts of the elastomer components in the core when a curing agent is included. The unsaturated carboxylic acids and metal salts thereof are generally soluble in the elastomeric base, or are readily dispersible. Examples of such commercially available curing agents include the zinc acrylates and zinc diacrylates available from Sartomer Company, Inc., 502 Thomas Jones Way, Exton, Pa.

A free radical initiator is optionally included in the elastomeric rubber composition; it is any known polymerization initiator (a co-crosslinking agent) which decomposes during the cure cycle. The term “free radical initiator” as used herein refers to a chemical which, when added to the elastomeric blend, promotes crosslinking of the elastomers. The amount of the selected initiator present is dictated only by the requirements of catalytic activity as a polymerization initiator. Suitable initiators include peroxides, persulfates, azo compounds and hydrazides. Peroxides which are readily commercially available are conveniently used in the present development, generally in amounts of from about 0.1 to about 10.0 and preferably in amounts of from about 0.3 to about 3.0 parts by weight per each 100 parts of elastomer, wherein the peroxide has a 40% level of active peroxide.

Exemplary of suitable peroxides are dicumyl peroxide, n-butyl 4,4′-bis (butylperoxy) valerate, 1,1-bis(t-butylperoxy)-3,3,5-trimethyl cyclohexane, di-t-butyl peroxide and 2,5-di-(t-butylperoxy)-2,5 dimethyl hexane and the like, as well as mixtures thereof. It will be understood that the total amount of initiators used will vary depending on the specific end product desired and the particular initiators employed.

Examples of such commercial available peroxides are Luperco™ 230 or 231 XL, a peroxyketal manufactured and sold by Atochem, Lucidol Division, Buffalo, N.Y., and Trigonox™ 17/40 or 29/40, a peroxyketal manufactured and sold by Akzo Chemie America, Chicago, Ill. The one hour half life of Luperco™ 231 XL and Trigonox™ 29/40 is about 112° C., and the one hour half life of Luperco™ 230 XL and Trigonox™ 17/40 is about 129° C. Luperco™ 230 XL and Trigonox™ 17/40 are n-butyl-4,4-bis(t-butylperoxy) valerate and Luperco™ 231 XL and Trigonox™ 29/40 are 1,1-di(t-butylperoxy) 3,3,5-trimethyl cyclohexane. Trigonox™ 42-40B is tert-Butyl peroxy-3,5,5-trimethylhexanoate and is available from Akzo Nobel; the liquid form of this agent is available from Akzo under the designation Trigonox™ 42S.

Preferred co-agents which can be used with the above peroxide polymerization agents include zinc diacrylate (ZDA), zinc dimethacrylate (ZDMA), trimethylol propane triacrylate, and trimethylol propane trimethacrylate, most preferably zinc diacrylate. Other co-agents may also be employed and are known in the art.

In further embodiments, the molded core includes a difunctional acrylate. It serves the dual function of being a curing agent and a co-agent to the free radical initiator. In specific embodiments, the molded core includes zinc diacrylate.

The elastomeric polybutadiene compositions of the present development can also optionally include one or more halogenated organic sulfur compounds which serve as a peptizer. The peptizer is usually a halogenated thiophenol of the formula below:

wherein R₁-R₅ are independently halogen, hydrogen, alkyl, thiol, or carboxylated groups. At least one halogen group is included, preferably 3-5 of the same halogenated groups are included, and most preferably 5 of the same halogenated groups are part of the compound. Examples of such fluoro-, chloro-, bromo-, and iodo-thiophenols include, but are not limited to pentafluorothiophenol; 2-fluorothiophenol; 3-fluorothiophenol; 4-fluorothiophenol; 2,3-fluorothiophenol; 2,4-fluorothiophenol; 3,4-fluorothiophenol; 3,5-fluorothiophenol; 2,3,4-fluorothiophenol; 3,4,5-fluorothiophenol; 2,3,4,5-tetrafluorothiophenol; 2,3,5,6-tetrafluorothiophenol; 4-chlorotetrafluorothiophenol; pentachlorothiophenol; 2-chlorothiophenol; 3-chlorothiophenol; 4-chlorothiophenol; 2,3-chlorothiophenol; 2,4-chlorothiophenol; 3,4-chlorothiophenol; 3,5-chlorothiophenol; 2,3,4-chlorothiophenol; 3,4,5-chlorothiophenol; 2,3,4,5-tetrachlorothiophenol; 2,3,5,6-tetrachlorothiophenol; pentabromothiophenol; 2-bromothiophenol; 3-bromothiophenol; 4-bromothiophenol; 2,3-bromothiophenol; 2,4-bromothiophenol; 3,4-bromothiophenol; 3,5-bromothiophenol; 2,3,4-bromothiophenol; 3,4,5-bromothiophenol; 2,3,4,5-tetrabromothiophenol; 2,3,5,6-tetrabromothiophenol; pentaiodothiophenol; 2-iodothiophenol; 3-iodothiophenol; 4-iodothiophenol; 2,3-iodothiophenol; 2,4-iodothiophenol; 3,4-iodothiophenol; 3,5-iodothiophenol; 2,4-iodothiophenol; 3,4-iodothiophenol; 3,5-iodothiophenol; 2,3,4-iodothiophenol; 3,4,5-iodothiophenol; 2,3,4,5-tetraiodothiophenol; 2,3,5,6-tetraiodothiophenol; and their metal salts thereof, and mixtures thereof. The metal salt may be salts of zinc, calcium, potassium, magnesium, sodium, and lithium. Another material is dodecanthiol.

In a specific embodiment, pentachlorothiophenol or zinc pentachlorothiophenol is included in the elastomeric composition. For example, RD 1302 of Rheim Chemie of Trenton, N.J. can be included therein. RD 1302 is a 75% masterbatch of Zn PCTP in a high-cis polybutadiene rubber.

Other suitable pentachlorothiphenols include those available from Dannier Chemical, Inc., Tustin, Calif., under the designation Dansof P™.

A representative metallic salt of pentachlorothiophenol is the zinc salt of pentachlorothiophenol (ZnPCTP) sold by Dannier Chemical, Inc. under the designation Dansof Z™.

The pentachlorothiophenol or metallic salt thereof is added in an amount of 0.01 to 5.0 parts by weight, preferably 0.1 to 2.0 parts by weight, more preferably 0.5 to 1.0 parts by weight, on the basis of 100 parts by weight of the elastomer.

In addition to the foregoing, filler materials can be employed in the compositions of the development to control the weight and density of the ball. Fillers which are incorporated into the compositions should be in finely divided form, typically in a size generally less than about 20 mesh, preferably less than about 100 mesh U.S. standard size. Preferably, the filler is one with a specific gravity of from about 0.5 to about 19.0. Examples of fillers which may be employed include, for example, silica, clay, talc, mica, asbestos, glass, glass fibers, barytes (barium sulfate), limestone, lithophone (zinc sulphide-barium sulfate), zinc oxide, titanium dioxide, zinc sulphide, calcium metasilicate, silicon carbide, diatomaceous earth, particulate carbonaceous materials, micro balloons, aramid fibers, particulate synthetic plastics such as high molecular weight polyethylene, polystyrene, polyethylene, polypropylene, ionomer resins and the like, as well as cotton flock, cellulose flock and leather fiber. Powdered metals such as titanium, tungsten, aluminum, bismuth, nickel, molybdenum, copper, brass and their alloys also may be used as fillers.

The amount of filler employed is primarily a function of weight restrictions on the weight of a golf ball made from those compositions. In this regard, the amount and type of filler will be determined by the characteristics of the golf ball desired and the amount and weight of the other ingredients in the core composition. The overall objective is to closely approach the maximum golf ball weight of 1.620 ounces (45.92 grams) set forth by the U.S.G.A.

The compositions of the development also may include various processing aids known in the rubber and molding arts, such as fatty acids. Generally, free fatty acids having from about 10 carbon atoms to about 40 carbon atoms, preferably having from about 15 carbon atoms to about 20 carbon atoms, may be used. Fatty acids which may be used include stearic acid and linoleic acids, as well as mixtures thereof. When included in the compositions of the development, the fatty acid component is present in amounts of from about 1 part by weight per 100 parts elastomer, preferably in amounts of from about 2 parts by weight per 100 parts elastomer to about 5 parts by weight per 100 parts elastomer. Examples of processing aids which may be employed include, for example, calcium stearate, barium stearate, zinc stearate, lead stearate, basic lead stearate, dibasic lead phosphite, dibutyltin dilaurate, dibutyltin dimealeate, dibutyltin mercaptide, as well as dioctyltin and stannane diol derivatives.

Furthermore, other additives known to those skilled in the art can also be included in the core components of the embodiments disclosed herein. These additions are included in amounts sufficient to produce the desired characteristics.

The core may be made by conventional mixing and compounding procedures used in the rubber industry. Different types and various amounts of materials are utilized to produce a molded core composition having the compression, resiliency, etc., properties desired. For example, the ingredients may be intimately mixed using, for example, two roll mills or a BANBURY® mixer, until the composition is uniform, usually over a period of from about 5 to 20 minutes. The sequence of addition of components is not critical. One blending sequence is as follows.

The elastomer, such as the polybutadienes, Cariflex® 1220, Neo-Cis® 60, Taktene®, or blends thereof, zinc pentachlorothiophenol (optional), and other components comprising the elastomeric rubber composition are blended for about 7 minutes in an internal mixer such as a BANBURY® mixer. As a result of shear during mixing, the temperature rises to about 200° F. The initiator and diisocyanate (optional) are then added and the mixing continued until the temperature reaches about 220° F. whereupon the batch is discharged onto a two roll mill, mixed for about one minute and sheeted out. The mixing is desirably conducted in such a manner that the composition does not reach incipient polymerization temperature during the blending of the various components.

The composition can be formed into a core by any one of a variety of molding techniques, e.g. compression, transfer molding, etc. If the core is compression molded, the sheet is then rolled into a “pig” and then placed in a BARWELL® preformer and slugs are produced. The slugs are then subjected to compression molding at about 320° F. for about 14 minutes. After molding, the molded cores are cooled at room temperature for about 4 hours or in cold water for about one hour. Usually the curable component of the composition will be cured by heating the composition at elevated temperatures on the order of from about 275° F. to about 350° F., preferably and usually from about 290° F. to about 325° F., with molding of the composition effected simultaneously with the curing thereof. When the composition is cured by heating, the time required for heating will normally be short, generally from about 10 to about 20 minutes, depending upon the particular curing agent used. Those of ordinary skill in the art relating to free radical curing agents for polymers are conversant with adjustments to cure times and temperatures required to effect optimum results with any specific free radical agent.

After molding, the core is removed from the mold and the surface may be treated to facilitate adhesion thereof to the covering materials. Surface treatment can be effected by any of the several techniques known in the art, such as corona discharge, ozone treatment, sand blasting, centerless grinding, and the like. Alternatively, the cores are used in the as-molded state with no surface treatment.

Further embodiments of the present invention may also include thermoplastic cores. These cores may comprise a highly neutralized ionomer (greater than 80%) and may comprise a fatty acid or fatty acid metal salt, such as disclosed in U.S. patent application Ser. No. 10/905,925, filed on Jan. 26, 2005, for a Golf Ball With Thermoplastic Material, which is hereby incorporated by reference in its entirety.

The resulting molded core generally has a diameter of about 1.0 to about 2.0 inches, preferably about 1.40 to about 1.60 inches and more preferably from about 1.520 to about 1.550 inches. Additionally, the weight of the core is adjusted so that the finished golf ball closely approaches the U.S.G.A. upper weight limit of 1.620 ounces. It has the high resiliency and hardness (i.e., high compression) desired. The molded core exhibits a COR of greater than 0.750, and preferably from about 0.780 to about 0.810, and more preferably from about 0.785 to about 0.805, and a compression (Instron) of greater than 0.0700, including from about 0.0750 to about 0.1300.

The mantle 14 of the golf ball of the present disclosure preferably comprises an ionomeric resin, more preferably a blend of high acid ionomer resins. Ionomeric resins are polymers containing interchain ionic bonding. They are generally ionic copolymers of an olefin, such as ethylene, and a metal salt of an unsaturated carboxylic acid, such as acrylic acid, methacrylic acid, or maleic acid. Metal ions, such as sodium, zinc, magnesium, etc., are used to neutralize some portion of the acidic group in the copolymer resulting in a thermoplastic elastomer exhibiting enhanced properties, such as increased durability and hardness. There are many commercial grades of ionomers available both from DuPont® and Exxon®, with a wide range of properties which vary according to the type and amount of metal cations, molecular weight, composition of the base resin (such as relative content of ethylene and methacrylic and/or acrylic acid groups) and additive ingredients such as reinforcement agents, and the like.

A suitable ionomer is a copolymer of an alpha-olefin and an alpha, beta-unsaturated carboxylic acid. The acid copolymer may contain anywhere from 1 to 30 percent by weight acid. A high acid copolymer containing greater than 16% by weight acid, preferably from about 17 to about 25 weight percent acid, and more preferably about 20 weight percent acid, or a low acid copolymer containing 16% by weight or less acid may be used as desired. The acid copolymer is neutralized with a metal cation salt capable of ionizing or neutralizing the copolymer to the extent desired, generally from about 10% to 100%. The amount of metal cation salt needed is that which has enough metal to neutralize up to 100% of the acid groups as desired.

Generally, the alpha-olefin has from 2 to 10 carbon atoms and is preferably ethylene, and the unsaturated carboxylic acid is a carboxylic acid having from about 3 to 8 carbons. Examples of such acids include, but are not limited to, acrylic acid, methacrylic acid, ethacrylic acid, chloroacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid. The carboxylic acid of the acid copolymer is, in embodiments, acrylic acid or methacrylic acid.

The ionomer mantle layer comprises any suitable ionomer resin having the characteristics desired. Examples of such suitable ionomer resins are commercially available from DuPont® under the designation Surlyn® or from Exxon® under the designation Iotek®. The ionomers preferably have a high flex modulus of from about 40 kpsi to about 100 kpsi, or from about 50 kpsi to about 85 kpsi, and in specific embodiments from about 60 kpsi to about 75 kpsi. The flex modulus is measured in accordance to ASTM 6272-98, with the test specimen conditioned for 14 days.

Further embodiments of the present invention may include intermediate layers comprising one or more ionomers which are neutralized to greater than 80%. The intermediate layer may also comprise ionomers comprising a fatty acid or fatty acid metal salt.

The various compositions of the mantle may be produced according to conventional melt blending procedures. In one embodiment, a simple dry blend of the pelletized or granulated copolymers which have previously been neutralized to a desired extent (and colored masterbatch, if desired) may be prepared and fed directly into the injection molding machine where homogenization occurs in the mixing section of the barrel prior to injection into the mold. If necessary, further additives, such as an inorganic filler, may be added and uniformly mixed before initiation of the molding process.

The resulting mantle has a Shore D hardness of from about 50 to about 80, including from about 60 to about 72, and in specific embodiments from about 67 to about 72. It has a resilience of from about 0.750 to about 0.830, including from about 0.805 to about 0.815, and about 0.810.

The outer layer, or cover layer 16, of the golf ball is a polyurethane cover. The polyurethane cover may be thermosetting or thermoplastic. The polyurethane material for the cover is composed of a diisocyanate and low monol content polyol. A polyurethane becomes irreversibly “set” when a polyurethane prepolymer is cross linked with a polyfunctional curing agent, such as a polyamine or a polyol. The prepolymer typically is made from polyether or polyester. Diisocyanate polyethers are sometimes preferred because of their water resistance.

The physical properties of thermoset polyurethanes are controlled substantially by the degree of cross linking. Tightly cross linked polyurethanes/polyureas are fairly rigid and strong. A lower amount of cross linking results in materials that are flexible and resilient. Thermoplastic polyurethanes have some cross linking, but primarily by physical means. The crosslinkings bonds can be reversibly broken by increasing temperature, as occurs during molding or extrusion.

Polyurethane covers can be formed in many ways. Generally, there is casting, reaction injection molding (“RIM”) and injection molding.

In a RIM process, highly reactive liquids are injected into a closed mold, mixed usually by impingement and/or mechanical mixing and secondarily mixed in an in-line device such as a peanut mixer, where they polymerize primarily in the mold to form a coherent, molded article. The RIM processes usually involve a rapid reaction between one or more reactive components such as the polyol and one or more isocyanate—containing constituents, often in the presence of a catalyst. The constituents are stored in separate tanks prior to molding and may be first mixed in a mix head upstream of a mold and then injected into the mold. The liquid streams are metered in the desired weight to weight ratio, such that the ratio of the —NCO groups to the active hydrogen groups is within a desired ration, and fed into an impingement mix head, with mixing occurring under high pressure, e.g., 1500 to 3000 psi. The liquid streams impinge upon each other in the mixing chamber of the mix head and the mixture is injected into the mold. One of the liquid streams typically contains a catalyst for the reaction. The constituents react rapidly after mixing to gel and form polyurethane polymers. Epoxies and various unsaturated polyesters also can be molded by RIM.

RIM differs from non-reaction injection molding processes in a number of ways. The main distinction is that in RIM a chemical reaction takes place in the mold to transform a monomer or adducts to polymers and the components are in liquid form. Thus, a RIM mold need not be made to withstand the pressures which occur in a conventional injection molding. In contrast, injection molding is conducted at high molding pressures in the mold cavity by melting a solid resin and conveying it into a mold, with the molten resin often being at about 150 to about 350° C. At this elevated temperature, the viscosity of the molten resin usually is in the range of 50,000 to about 1,000,000 centipoise, and is typically around 200,000 centipoise. In an injection molding process, the solidification of the resins occurs after about 10 to 90 seconds, depending upon the size of the molded product, the temperature and heat transfer conditions, and the hardness of the injection molded material. Subsequently, the molded product is removed from the mold. There is no significant chemical reaction taking place in an injection molding process when the thermoplastic resin is introduced into the mold. In contrast, in a RIM process, the chemical reaction typically takes place in less than about 2 minutes, preferably in under one minute, and in many cases in about 30 seconds or less.

The fast-chemical-reaction-produced component can incorporate suitable additives and/or fillers. When the component is an outer cover layer, pigments or dyes, accelerators and UV stabilizers can be added. Examples of suitable optical brighteners which probably can be used include Uvitex™ and Eastobrite™ OB-1. An example of a suitable white pigment is titanium dioxide. Examples of suitable and UV light stabilizers are provided in commonly assigned U.S. Pat. No. 5,494,291.

Fillers which can be incorporated into the fast-chemical-reaction-produced cover or core component include those listed below in the definitions section. Furthermore, compatible polymeric materials, such as polyurethane ionomers, polyamides, etc., can be added.

Catalysts can be added to the RIM polyurethane/polyurea system starting materials as long as the catalysts generally do not react with the constituent with which they are combined. Suitable catalysts include those which are known to be useful with polyurethanes and polyureas. These catalysts include dibutyl tin dilaurate or triethylenediamine.

The reaction mixture viscosity should be sufficiently low to ensure that the mold is completely filled. The reactant materials generally are preheated to about 80° F. to about 200° F. and preferably to 100° F. to about 180° F. before they are mixed. In most cases it is necessary to preheat the mold to, e.g., from about 80° F. to about 200° F., to provide for proper injection viscosity and system reactivity.

Molding at lower temperatures is beneficial when, for example, the cover is molded over a core. Normally, at higher temperature molding processes, the core may expand during molding. Such core expansion is not of such a concern when molding at lower temperatures utilizing RIM.

Several chemical reactions may occur during polymerization of isocyanate and polyol. Isocyanate groups (—N═C═O) that react with alcohols form a polyurethane.

The polyol component typically contains additives, such as stabilizers, flow modifiers, catalysts, combustion modifiers, blowing agents, fillers, pigments, optical brighteners, surfactants and release agents to modify physical characteristics of the cover. Polyurethane constituent molecules that were derived from recycled polyurethane can be added in the polyol component.

Cross linking occurs between the isocyanate groups (—NCO) and the polyol's hydroxyl end-groups (—OH). Additionally, the end-use characteristics of polyurethanes can also be controlled by different types of reactive chemicals and processing parameters. For example, catalysts are utilized to control polymerization rates. Depending upon the processing method, reaction rates can be very quick (as in the case for some reaction injection molding systems (i.e., RIM).

Any suitable polyisocyanate may be used to form a polyurethane according to the exemplary embodiment. The polyisocyanate is preferably selected from the group of diisocyanates including, but not limited, to 4,4N-diphenylmethane diisocyanate (“MDI”); 2,4-toluene diisocyanate (“TDI”); m-xylylene diisocyanate (“XDI”); methylene bis-(4-cyclohexyl isocyanate) (“HMDI”); hexamethylene diisocyanate (HDI); naphthalene-1,5,-diisocyanate (“NDI”); 3,3N-dimethyl-4,4N-biphenyl diisocyanate (“TODI”); 1,4-diisocyanate benzene (“PPDI”); phenylene-1,4-diisocyanate; and 2,2,4- or 2,4,4-trimethyl hexamethylene diisocyanate (“TMDI”).

Other less preferred diisocyanates include, but are not limited to, isophorone diisocyanate (“IPDI”); 1,4-cyclohexyl diisocyanate (“CHDI”); diphenylether-4,4N-diisocyanate; p,pN-diphenyl diisocyanate; lysine diisocyanate (“LDI”); 1,3-bis (isocyanato methyl)cyclohexane; and polymethylene polyphenyl isocyanate (“PMDI”).

One polyurethane component which can be used in the exemplary embodiment incorporates TMXDI (META) aliphatic isocyanate (Cytec Industries, West Paterson, N.J.). Polyurethanes based on meta-tetramethylxylylene diisocyanate can provide improved gloss retention, UV light stability, thermal stability and hydrolytic stability. Additionally, TMXDI (META) aliphatic isocyanate has demonstrated favorable toxicological properties. Furthermore, because it has a low viscosity, it is usable with a wider range of diols (to polyurethane) and diamines (to polyureas). If TMXDI is used, it typically, but not necessarily, is added as a direct replacement for some or all of the other aliphatic isocyanates in accordance with the suggestions of the supplier. Because of slow reactivity of TMXDI, it may be useful or necessary to use catalysts to have practical demolding times. Hardness, tensile strength and elongation can be adjusted by adding further materials in accordance with the supplier's instructions.

The polyurethane which is selected for use as the golf ball cover preferably has a Shore D hardness of 20 to 80, more preferably 50 to 70, and most preferably 60 to 68. Alternatively, Shore B can be utilized to characterize the cover hardness. Comparably, Shore B values are from about 50 to about 100, including from about 70 to about 100 and from about 80 to about 100. The polyurethane which is to be used for a cover layer preferably has a flex modulus of 1 to 310 kpsi, more preferably 5 to 100 kpsi, and most preferably 5 to 20 kpsi for a soft cover layer and 30 to 100 kpsi for a hard cover layer.

The resulting golf ball 10 of the present disclosure has the desired characteristics noted above. It has a diameter of 1.680 inches or more, the minimum permitted by the U.S.G.A; oversize balls may be produced if desired. In some embodiments, the diameter of the golf ball is from 1.680 inches to about 1.780 inches. It weighs no more than 1.62 ounces. It has low driver spin and good green-side spin. It has a high initial velocity of between 250 and 255 feet/sec. It has a COR of from about 0.770 to about 0.820, including from about 0.790 to about 0.816, and from about 0.805 to about 0.816. A more detailed description of a golf ball having a high COR is set forth in U.S. Pat. No. 6,443,858, for a Golf Ball With A High Coefficient Of Restitution, and in U.S. Pat. No. 6,478,697 for a Golf Ball With A High Coefficient Of Restitution, both of which are hereby incorporated by reference in their entireties.

The surface geometry of the golf ball is preferably a conventional dimple pattern such as disclosed in U.S. Pat. No. 6,213,898 for a Golf Ball With An Aerodynamic Surface On A Polyurethane Cover, which pertinent parts are hereby incorporated by reference. Alternatively, the surface geometry of the golf ball has a non-dimple pattern such as disclosed in U.S. Pat. No. 6,290,615 for A Golf Ball Having Tubular Lattice Pattern, or U.S. Pat. No. 6,979,272, for an Aerodynamic Surface Geometry Of A Golf Ball, both of which pertinent parts are hereby incorporated by reference.

Specifically, the arrangement and total number of dimples are not critical and may be properly selected within ranges that are well known. For example, the dimple arrangement may be an octahedral, dodecahedral or icoshedral arrangement. The total number of dimples is generally from about 250 to about 600, and especially from about 300 to about 500. The dimples may also be hexagonal in shape.

Additionally, one or more deep dimples may also be included to enhance the molded golf ball construction process and/or aerodynamics. A deep dimple is a dimple that extends through the cover material to the intermediate or mantle layer and/or to the core. For example, six extra deep hexagonal dimples may be included to help to balance lift and drag. The extra deep dimples may also be included to enhance the centering of the ball during ball construction. Deep dimples are disclosed in U.S. Pat. No. 6,790,149 for a Golf Ball, which is hereby incorporated by reference in its entirety.

In other embodiments, the golf ball is coated with a durable, abrasion-resistant, relatively non-yellowing finish coat or coats if necessary. The finish coat or coats may have some optical brightener and/or pigment added to improve the brightness of the finished golf ball. In one embodiment, from 0.001 to about 10% optical brightener may be added to one or more of the finish coatings. If desired, optical brightener may also be added to the cover materials. One type of preferred finish coatings are solvent based urethane coatings known in the art. It is also contemplated to provide a transparent outer coating or layer on the final finished golf ball. Golf balls also typically include logos and other markings printed onto the dimpled spherical surface of the ball. Paint, typically clear or white pigmented paint, is applied for the purposes of protecting the cover and improving the outer appearance before the ball is completed as a commercial product.

From the foregoing it is believed that those skilled in the pertinent art will recognize the meritorious advancement of this invention and will readily understand that while the present invention has been described in association with a preferred embodiment thereof, and other embodiments illustrated in the accompanying drawings, numerous changes, modifications and substitutions of equivalents may be made therein without departing from the spirit and scope of this invention which is intended to be unlimited by the foregoing except as may appear in the following appended claims. Therefore, the embodiments of the invention in which an exclusive property or privilege is claimed are defined in the following appended claims. 

1. A multi-layer golf ball comprising: a core; an intermediate layer; and, a polyurethane cover, the polyurethane cover comprising a low-monol content polyol and a diisocyanate, wherein the low-monol content polyol has a monol content of less than 1%.
 2. The multi-layer golf ball of claim 1, wherein the ball has an Instron compression of 0.0920 or less.
 3. The multi-layer golf ball of claim 1, wherein the cover of the ball has a thickness of 0.050 inches or less.
 4. The multi-layer golf ball of claim 1, wherein the cover of the ball has a thickness of 0.025 inches or less.
 5. The multi-layer golf ball of claim 1, wherein the cover of the ball has a thickness of from about 0.012 inches to about 0.018 inches.
 6. The multi-layer golf ball of claim 1, wherein the cover of the ball has a Shore B hardness of from about 50 to about
 100. 7. The multi-layer golf ball of claim 1, wherein the cover of the ball has a Shore B hardness of from about 80 to about
 95. 8. The golf ball of claim 1, wherein the polyurethane cover comprises an ultra low monol content poly(propylene glycol).
 9. The golf ball of claim 1, wherein the mantle comprises an ionomer or a blend of ionomers.
 10. The golf ball of claim 9 where the ionomer or blend further comprises a fatty acid or fatty acid metal salt.
 11. The golf ball of claim 1, wherein the polyurethane cover comprises an ultra low monol content tri(propylene glycol).
 12. The golf ball of claim 1, wherein the cover is coated with a coating composition comprising a white pigment.
 13. The golf ball of claim 1, wherein a marking indicia is applied to the exterior surface of the ball.
 14. The golf ball of claim 1, wherein said core is produced from a core composition comprising an organic sulfur compound.
 15. The golf ball of claim 14, wherein the organic sulfur compound is PCTP or a metal salt thereof.
 16. A multilayer golf ball, comprising: a molded rubber core; an intermediate layer between the cover and the core that has a Shore D hardness measurement of greater than 60; and a thermosetting polyurethane cover having a thickness of from about 0.010 inches to about 0.050 inches, the thermosetting polyurethane cover formed from a low-monol content polyol, wherein the low-monol content polyol has a monol content of less than 1%.
 17. The multi-layer golf ball of claim 16, wherein the ball has an Instron compression from about 0.0800 to about 0.0950.
 18. The multi-layer golf ball of claim 16, wherein the cover of the ball has a thickness of 0.025 inches or less.
 19. The multi-layer golf ball of claim 16, wherein the cover of the ball has a thickness of from about 0.012 inches to about 0.018 inches.
 20. The multi-layer golf ball of claim 16, wherein the cover of the ball has a Shore B hardness of from about 80 to about
 95. 